Young Blood Makes Muscles Spry

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Young Blood Makes Muscles Spry

Researchers at Stanford University have found that an infusion of young blood has significant benefits.

It's not a figure of speech. The scientists linked the blood supply of young mice to old mice, and what they found will have an impact on stem-cell research as well as the scientific study of aging: The young blood activated stem cells in the old muscles that allowed them to recover from injury like a spring chicken.

Longevity enthusiasts shouldn't get too excited just yet. Hooking a young human's blood supply up to an old person would throw both immune systems into chaos (the mice were modified to be genetically identical). But the results, published in the Feb. 17 issue of Nature, are exciting for stem-cell researchers and tissue-regeneration scientists looking for therapies in everything from elderly care to spinal-cord injury.

"It's not so much about making people live longer," said Dr. Thomas Rando, associate professor of neurology at Stanford University School of Medicine. "But if some older person gets a broken bone or skin wound, maybe we could improve their recovery rate. Maybe there's a chance to enhance the potential of old tissues."

If you're thinking a blood transfusion will offer the same effects, think again. The old mice shared their younger counterparts' blood supply for six weeks.

"In terms of magnitude and duration, that's vastly greater than a transfusion," Rondo said. "You're not going to see this kind of effect."

If the researchers want to translate this work into a treatment for aging muscles or other tissues, they must pinpoint the youth-inducing molecules in the blood that are responsible for switching on the stem-cell capabilities in old muscles. Rando said that grueling process will be his lab's next project.

The discovery could have more immediate implications for stem-cell research. The results show that as researchers begin to test stem-cell therapies, they need to pay close attention to the environment into which they're thrusting the cells: If the stem cells do not perform the desired task, the surroundings rather than the stem cells themselves might be to blame.

Rando and his colleagues studied muscle stem cells called satellite cells, which in young mice and humans induce repair when injury strikes. Rando found in previous work that satellite cells exist in older muscle, but they don't respond to a muscle's cry for help after injury. In the new study, the presence of younger blood helped the satellite cells work more like they do in young mice.

A previous discovery from Rando's lab helped confirm the latest findings. The researchers found that satellite cells in younger muscles increase production of a protein called Delta in response to muscle injury. But older muscles didn't produce any extra Delta after muscle damage. In the Nature study, the old mice infused with young blood produced youthful levels of Delta post-injury, and vice versa: Young satellite cells produced less Delta when exposed to older blood.

The findings will affect disparate fields – including research into stem cells, muscle injury, tissue regeneration and aging – but there are synergies to be found as well, Rando said.

"Many stem-cell applications in people include diseases of old people," he said. "So if the environment of the heart, brain, liver (and) pancreas is less conducive (to healing) than that of a young person, it would be important to know that in advance."